Stents are generally tubular shaped implantable devices that are expand radially to hold open a segment of a blood vessel after implantation into an anatomical lumen. Stents are generally introduced into the anatomical lumen by a stent delivery device, such as a catheter assembly. It has been found that polymer coated stents are advantageous in providing the intravascular stent with a smooth surface and can be utilized to serve as a vehicle or carrier of therapeutic agent. In this regard, the coated stents often contain multiple layers of polymer material applied to the surface of the stent.
A well-known method for manufacturing a coated stent involves applying a polymer coating onto the desired surface of the stent by dipping or spraying techniques, for example, or other known techniques.
In addition to multilayered stents, other medical devices such as stent delivery devices also include components that can be coated or multilayered. For example, U.S. Pat. No. 6,663,614 to Carter, which is incorporated herein in its entirety, discloses a catheter shaft having at least two polymeric layers to provide better pushability and/or a variable flexibility along the length of the catheter shaft. As yet another example, U.S. Pat. No. 7,025,752 to Rice, the entire content of which is incorporated herein, discloses a balloon having multiple coatings of lubricious material. Accordingly, many different types of multilayered medical devices are currently utilized in medical applications.
One drawback in the process of manufacturing multilayered medical devices, such as coated stents or multilayered catheter shafts is poor adhesion of the multiple polymeric coatings to each other or to the surface of the medical device. For example, and as described in U.S. Pat. No. 6,805,898 to Wu, which is incorporated herein in its entirety, discloses that a poorly adhered coating on a stent can be rubbed and peeled off of the stent if the coating contacts an arterial wall while the stent is being moved into position. Wu further discloses that the problem of poorly adhered coating material can promote thrombosis and restenosis, by providing additional surfaces for platelets and other blood components to adhere and can lead the loss of a significant amount of the drugs to be delivered from the coating.
Wu attempts to solve the problem of poorly adhesion by providing a medical device such as a stent or graft with asperities on the outer surface to improve retention of one or more layers of coatings on the device. According to Wu, the asperities are formed on the surface of the medical device by the removal of material by chemical etching techniques.
Thus, there remains a need for efficient and economic systems and methods for manufacturing a coated or multilayered medical device, which will also improve adhesion properties of the coating or multiple layers to the medical device.